A major desire presently expressed by motor vehicle manufacturers is to maximize capacity.
Thus, inside the cabin, manufacturers are seeking to increase the distance between two facing doors both for ergonomic and for stylistic reasons.
Naturally, one way of increasing capacity is to reduce the thickness of the door capping. However that must be done without nevertheless diminishing performance in terms of safety.
The term “door capping” is used herein to mean longitudinally extending members that extend parallel to the longitudinal axis of the vehicle and that are integrated in the thickness of the door. These are hollow elements, generally constituted by assembling together two sections, and they contribute in non-negligible manner to absorbing a fraction of the energy received by the door during an impact that results from a collision.
In such a lateral impact, the involvement of the door capping in absorbing energy is variable.
Given the various types of impact, it can be advantageous to adapt the stiffness of the structure so as to optimize its capacity to absorb impact energy.
Thus, in the event of a relatively gentle lateral impact, it is useful for the capping to retain its initial shape, whereas in the event of a more violent impact, it is essential for the energy absorption capacities of the capping to be increased.
Documents U.S. Pat. No. 5,382,051, DE-A-10 022 094, GB-A-2 362 138, U.S. Pat. No. 5,845,937, and U.S. Pat. No. 5,615,914 describe systems that enable integral or fitted elements of the bodywork of a motor vehicle to deform in such a manner as to increase their capacity for absorbing energy in the event of an impact being detected.
To do this, those elements have their moment of inertia increased by increasing their section. The systems implemented also make provision for this increase in section to be obtained by increasing the pressure inside the element. The increase in pressure is obtained by producing gas as a result of the combustion of a pyrotechnic material.
In practice, the technique implemented is similar to that which is encountered when inflating an airbag.
A first drawback that results from that practice is that the pressure inside the element must increase sufficiently to deform the structure. Consequently, a large quantity of gas must be generated, which likewise requires a large quantity of pyrotechnic material.
In addition, when the walls of the element deform as a result of the increase in pressure, it is necessary to continue to produce the gas in order to compensate for the increase in volume.
Under such conditions, the time that elapses between detecting an impact and the bodywork element being effectively deformed is of the order of about ten to a few tens of milliseconds.
Unfortunately, that time is too long for said deformation to have full effectiveness.
The present invention seeks to mitigate those drawbacks, while relying on technology that is simple, and that does not depart completely from the means that have been used until now.
A first aspect of the present invention thus relates to a device for reinforcing a hollow motor vehicle bodywork element of closed right section, the device being characterized by the fact that said element has means suitable for subjecting its inside space to a shock wave or pressure wave on detecting an impact, such that the energy generated by said wave is sufficient to deform the element by increasing its section.
According to other characteristics of the device that are advantageous but not limiting: said means comprise a pyrotechnic material; said pyrotechnic material is in the form of at least one detonating or deflagrating cord; said pyrotechnic material is in the form of an explosive coating applied to its inside surface; it is coupled to a gas generator containing said pyrotechnic material, the gas generated by the combustion of said material being released into said element, the resulting pressure wave inside said element being sufficient on its own to deform the element by increasing its section; and it includes means for stiffening the hollow element after it has deformed.
A second aspect of the present invention relates to a method of deforming a hollow motor vehicle bodywork element, said element being of closed right section, in such a manner as to increase its capacity to absorb energy during an impact.
The method is essentially characterized by the fact that, on detecting said impact, it consists in subjecting the inside space of the element to a shock or pressure wave, such that the energy generated by said wave is sufficient to deform the element by increasing its section.
This wave which manifests a pressure difference propagates in a very short length of time, of the order of one to a few milliseconds, typically of the order of less than five milliseconds.
This duration makes the deformation of the element fully effective in its capacity to absorb a large quantity of energy resulting from an impact.
According to other characteristics of the method that are advantageous but not limiting: said wave is generated by using a pyrotechnic material; said wave is generated by means of at least one detonating or deflagrating cord placed in the inside space of said element; said inside space is lined with a solid padding material in which said cord is placed; said padding material is a polymer, a granular medium, or a foam; said wave is generated using an explosive coating applied to the inside surface of said element; said coating is applied in register solely with the or each zone of the inside surface of said element that is to be deformed; and a gas generator is used that contains said pyrotechnic material, the gas generated by combustion of said material being released into said element, the pressure wave as obtained in this way inside said element sufficing on its own to deform the element by increasing its section.